The present invention relates generally to a coated medical device and more particularly to a coated stent. Stents, grafts, stent-grafts, vena cava filters and similar implantable medical devices, collectively referred to hereinafter as stents, are radially expandable endoprostheses which are typically implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. Stents may be implanted in a variety of body lumens or vessels such as within the vascular system, esophagus, gastrointestinal tract, large and small intestine, biliary ducts, pancreas ducts, pulmonary and urinary tracts, etc. Stents may be used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. Stents may also be used to open strictures. They may be self-expanding, mechanically expandable or hybrid expandable.
Stents are typically tubular members that are radially expandable from a reduced diameter configuration for delivery through a patient's body lumen to an expanded configuration once deployed at the treatment site.
Stents may be constructed from a variety of materials such as stainless steel, Elgiloy®, nickel, titanium, nitinol, shape memory polymers, other polymeric materials, etc. For metallic stents, a stent may be typically braided or woven from singular or multiple filaments in the form of a tubular member, either extruded or formed from a sheet, in which a pattern is subsequently formed by etching or cutting material from the tubular member.
Polymeric stents formed from a variety of thermoplastic polymer materials may be formed by weaving or braiding fibers or filaments.
Stents may further be provided with a cover, such as a silicone cover to prevent tissue ingrowth.
Desirable stent properties include sufficient flexibility to be able to conform to the tortuous body lumen during delivery, yet sufficiently rigid to resist migration once deployed at the treatment site.
In some stents, the compressible and flexible properties that assist in stent delivery may also result in a stent that has a tendency to migrate from its originally deployed position. Stent covering may contribute to migration as well. Stent migration affects many endoscopic stents including esophageal, pancreatic and biliary stents. Risk factors associated with stent migration are discussed in Incidence and risk factors for biliary and pancreatic stent migration, Johanson JF, Schmah. MJ, Geenen JE. Gastrointest Endosc. 1992 May-Jun;38(3):341-6.
It is thus desirable to provide a stent configuration that resists migration following deployment.
Esophageal stents are particularly susceptible to stent migration due to the structure of the esophagus and conditions therein such as peristalsis.
Moreover, fully covered stents prevent tissue ingrowth and are easier to remove than bare or partially covered stents. However, these stents are even more prone to migration. The migration rate for a fully covered stent in pulmonary and esophageal indication is about 20-50%.
It is thus desirable to provide a stent configuration that resists migration following deployment.
One way to reduce the risk of stent migration has been to expose bare metal portions of the stent to esophageal tissue. The open structure of the stent provides a scaffold that promotes tissue ingrowth into the stent. This tissue ingrowth anchors the stent in place and greatly reduces the risk of migration. However, tissue ingrowth may lead to reocclusion of the lumen. In addition, stents anchored by tissue ingrowth cannot be moved or removed without an invasive procedure. To reduce tissue ingrowth, stents have been covered with a polymer coating to create a physical barrier between the stent lumen and the tissue wall. However, traditional polymer coated esophageal stents have higher rates of migration than their bare metal counterparts.
Another way to reduce the risk of stent migration has been to use a flared stent. However, stents are susceptible to migration even with flares.
Another method of reducing stent migration has been to provide surface features such as bumps or protrusions or other surface features such as disclosed in US Patent Publication Nos. 2006/0069425 and 2009/0062927, and in commonly assigned 2012/0035715, each of which is incorporated by reference herein in its entirety.
Commonly assigned US Patent Publication No. 2009/0098176, the entire content of which is incorporated by reference herein, discloses medical devices with triggerable bioadhesives.
Many techniques have been developed to prevent stent migration including adding barbs and flares to the stent itself or using clips or sutures to attach the stent to the vessel wall.
There remains a need in the art for an improved stent that is resistant to migration.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.